JPH04325428A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To produce an optical fiber preform at the time of drawing a first preform into a second preform rod having a smaller diameter than the former by detecting the tension of the first rod and controlling the power to be supplied to a drawing furnace so that the rod is drawn always with a fixed tension. CONSTITUTION:A first preform rod 1 is passed through a drawing furnace 3 and drawn into a second preform rod 2 having a smaller diameter than the former to produce an optical fiber preform. In this case, a tension detector is provided on the first rod 1 holding means side, and the power to be supplied to the furnace 3 is controlled in accordance with the detected tension of the first rod 1. Consequently, the first rod 1 is drawn with a fixed tension, and the optical fiber is produced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a first base material rod,
When drawing a second base material rod with a smaller diameter, the tension in the first base material rod is detected and the power input to the drawing furnace is controlled so that the drawing is always at a constant stretching tension. The present invention relates to a method for manufacturing an optical fiber preform.

0002

BACKGROUND OF THE INVENTION Conventionally, in order to draw a first base material rod (for example, a glass rod) into a second base material rod having a smaller diameter, it has been introduced into a drawing furnace (such as an electric furnace). The base material is softened by heating, and in this state it is stretched.

[0003] At this time, power is generally applied to the drawing furnace at a constant value over the entire length of the first base material rod, that is, from the start to the end of drawing.

0004

[Problem to be Solved by the Invention] However, according to research conducted by the present inventors, it has been found that the above method has a problem in that it is not possible to stretch with a constant stretching tension when considering the actual properties of the base material and the properties of the furnace itself. It was done. In other words, it has been found that in actual base materials, the outer diameter is not always uniform over the entire length in the longitudinal direction, but there are subtle variations, making it impossible to stretch with a constant stretching tension.

Furthermore, even if the outer diameter of the first base material rod is uniform over its entire length, the stretching tension gradually decreases immediately after the stretching starts due to the characteristics of the furnace itself (such as properties such as thermal conductivity). This tendency was observed, and it was found that the method of constantly supplying constant electric power does not allow stretching at a constant stretching tension.

The present invention has been made in view of such conventional circumstances.

[Means for Solving the Problems] The present invention is characterized in that a first base material rod is passed through a drawing furnace and stretched to a second base material rod having a smaller diameter to form an optical fiber. In the method for manufacturing a base material, a tension detection device is provided on the holding means side of the first base material rod, and power input to the drawing furnace is controlled according to the detected tension of the first base material rod. , a method for manufacturing an optical fiber preform in which the stretching tension of the first preform rod is kept constant.

[0007]

[Operation] In this way, the tension of the first base material rod is detected,
By controlling the input power according to this detected tension, it is possible to manufacture an optical fiber preform with a constant drawing tension regardless of changes in the outer diameter of the rod or characteristics of the furnace.

[0008]

Embodiment FIGS. 1 and 2 show an embodiment of the method for manufacturing an optical fiber preform according to the present invention.

In the figure, 1 is a first base material rod, and 2 is a first base material rod that is passed through a drawing furnace 3 and
This is a second preform rod extending to a smaller diameter than the preform rod 1, and the desired optical fiber preform is obtained from this second preform rod.

The drawing furnace 3 is an electric furnace, and includes an internal cylindrical muffle 4 and a heating element 5 such as an electric heater that heats the first base material rod 1 through the muffle 4.

As shown in FIG. 1, dummy rods 6 and 7 are connected to the upper end of the first base material rod 1 and the lower end of the second base material rod 2, respectively. , this delivery side dummy rod 6 is connected to the chuck 8
The dummy rod 7 on the receiving side is supported via the tension detection unit 9 and the hanging member 10 by the sending device 12 which is slidably attached to the guide rails 11 and 11. It is also supported by a take-off device 14 which is slidably mounted on the guide rails 11,11.

To be more specific, the tension detecting section 9 is as shown in FIG. 3, for example, and has tension detecting devices 15, 15 such as load cells built in between upper and lower flat plates 9a, 9b.

In the drawing furnace 3 thus constructed,
The first base material rod 1 is sent out at a predetermined speed V1 from its initial outer diameter D, and is stretched while being softened by heating in the drawing furnace 3, and the second base material rod 1 has a target outer diameter (diameter) d0.
However, in the case of the present invention, the stretching tension of the first base material rod 1 at that time is determined by the tension detection devices 15 as follows. It can be detected at all times through equation (1).

That is, the load W determined by the tension detection devices 15, 15 is the sum of the stretching tension F of the first base material rod 1 and the weight of the base material, so the following relationship holds true. F=W-(D/2)2 ・π・l・ρ
(
1) However, in the same formula, D: original base material diameter, π: pi, l
: Feeding length of the original base material, ρ: Base material rod (=2.2 in case of quartz glass rod).

According to the present invention, during actual operation of the drawing furnace 3, the tension of the first base material rod is detected by the tension detection devices 15, 15, and according to the detected tension,
Control input power. For example, when the tension becomes larger than a desired reference value, the input power is increased, and when the tension becomes smaller, the input power is decreased.

In other words, when the tension of the first base material rod is high, it receives a larger amount of heat, promoting the softening of the rod itself, and controlling the tension in a direction that decreases, and when the tension is low, the amount of heat decreases. , the softening of the rod itself is slowed down and the tension is controlled in an increasing direction, and as a whole, the stretching tension of the first base material rod 1 remains almost constant without being affected by its outer diameter or the characteristics of the furnace. and ideal stretching can be obtained. Due to this uniform stretching tension, the obtained optical fiber is free from distortion and has extremely good transmission characteristics.

In the above embodiment, the tension detecting device 15 such as a load cell is built into the tension detecting section 9, but the present invention is not limited to this, and other tension detecting devices may be used. , it is also possible to set it in another location.

[0018]

[Effects of the Invention] As described above, according to the method of manufacturing an optical fiber according to the present invention, the tension of the first base material rod is detected and the input power is controlled according to the detected tension. It is possible to manufacture an optical fiber preform with constant drawing tension regardless of changes in the rod outer diameter or furnace characteristics.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an example of an apparatus system for implementing an optical fiber manufacturing method according to the present invention.

FIG. 2 is a schematic vertical sectional view showing a drawing furnace in the apparatus system of FIG. 1;

FIG. 3 is a partial vertical sectional view showing a built-in tension detection section of the tension detection device in the device system of FIG. 1;

[Explanation of symbols]

Claims (1)

[Claims] Claim 1: Passing a first base material rod through a drawing furnace;
In a method for producing an optical fiber preform by stretching a second preform rod having a smaller diameter, a tension detection device is provided on the holding means side of the first preform rod, and A method for manufacturing an optical fiber preform, comprising controlling input power to the drawing furnace according to the detected tension to keep the drawing tension of the first preform rod constant.